I. FIELD OF THE INVENTION
The present invention is directed to topical preparation systems which are high internal phase water-in-oil emulsions. Specifically, the invention is concerned with high internal phase water-in-oil emulsions which are commercially stable.
II. DESCRIPTION OF THE PRIOR ART
It has been found advantageous to formulate topical preparations in high internal phase ratio water-in-oil systems. Topical preparations include cosmetic and/or pharmaceutical products which are applied to external skin areas. By incorporating active agents desirable for topical use in high internal phase ratio water-in-oil emulsions, a number of advantages are obtained. Such advantages include the obtaining of an oil adherent system without utilizing high concentrations of oil.
A method of preparing a water-in-oil high internal phase ratio topical emulsion is described in United Kingdom Pat. No. 1,415,528 which is incorporated by reference herein. The emulsions disclosed in the patent do not display commercial stability. That is, they fail to remain emulsified for more than five freeze-thaw cycles. A freeze-thaw cycle is defined as the freezing of a sample of an emulsion at 14.degree. F. for 24 hours and then allowing it to thaw at room temperature, 72.degree. F., for 24 hours. Freeze-thaw cycles simulate conditions which may be encountered during transportation and/or storage of a product. For an emulsion to be commercially acceptable, it must survive at least five freeze-thaw cycles.
As discussed above, it has been possible to formulate water-in-oil high internal phase ratio topical emulsions which demonstrate limited noncommercial stability. The most commonly used emulsifier in these formulations is POE(2) oleyl ether which is oleic acid that has been oxyalkylated with two moles of ethylene oxide.
The present invention is advantageous in that it provides a nonlipoidal media in lipoidal media high internal phase ratio emulsion which is stable for extended periods, even at elevated temperatures. Further, the invention is advantageous since it provides a nonlipoidal media in lipoidal media high internal phase ratio emulsion which does not break or leak after five freeze-thaw cycles and remains on the skin for extended periods while being cosmetically acceptable.